Polymer polyols (PMPOs) are employed in the preparation of polyurethane foams and elastomers and are extensively used on a commercial scale. Polyurethane foams made from such polymer polyols have a wide variety of uses. The two major types of polyurethane foams are slabstock and molded foam. Polyurethane slabstock foams are used in carpet, furniture and bedding applications. Molded polyurethane foams are used in the automotive industry for a broad range of applications.
Polymer polyols are typically produced by polymerizing one or more ethylenically unsaturated monomers dissolved or dispersed in a prepared polyol in the presence of a free radical catalyst to form a stable dispersion of polymer particles in the polyol. Typically, polymer polyols used to produce polyurethane foams having higher load-bearing properties than those produced from unmodified polyols were prepared using acrylonitrile monomer; however, many of those polymer polyols have undesirably high viscosity.
Polyurethane foams having high load-bearing properties are predominantly produced using polymer polyols that are prepared from a high styrene content monomer mixture (for example, 65 to 75 percent styrene). However, polymer polyols produced from such high styrene monomer mixtures often fail to satisfy the ever more demanding needs of industry, including acceptable viscosity, strict stability requirements and increased load-bearing properties.
Stability and low viscosity of polymer polyols are of increasing importance to polyurethane foam manufacturers due to the development of sophisticated, high speed and large volume equipment and systems for handling, mixing and reacting polyurethane-forming ingredients. Polymer polyols must meet certain minimum polymer particle size requirements to avoid plugging or fouling filters, pumps and other parts of such foam processing equipment in relatively short periods of time.
Numerous attempts have been made to produce polymer polyols that will satisfy the above criteria. In particular, Japanese laid-open patent application, Kokai No. 6-228247, teaches a semibatch process for making a polymer polyol by the sequential addition of oxide monomer and its polymerization followed by addition of vinyl monomers and their polymerization in the same reactor. Although the Japanese laid-open application teaches that removal of the DMC catalyst is not required, it fails to even suggest that the processing steps could be anything other than sequential. Thus, while one skilled in the art might infer from reading Kokai '247 that DMC catalysts do not interfere with free radical polymerization, Kokai '247 provides no guidance concerning whether free radical polymerization interferes with DMC catalysis.
A number of workers have patented continuous processes for producing polyols, such as U.S. Pat. No. 5,689,012, issued to Pazos et al., which discloses a continuous process for the preparation of polyoxyalkylene polyethers using DMC catalysts as the polyoxyalkylation catalyst and employing continuous addition of alkylene oxide in conjunction with continuous addition of starter and catalyst to a continuous oxyalkylation reactor. The polyether products are said to be exceptionally well suited for use in polymer forming systems, particularly polyurethanes. In the process of Pazos et al., polyol synthesis begins with introduction of catalyst/starter into the continuous reactor, initiation of oxyalkylation, and while oxyalkylation progresses, continuous addition of catalyst, starter and alkylene oxide with continuous removal of polyol product. The process of Pazos et al. adds “fresh” catalyst or pre-activated catalyst.
U.S. Pat. No. 5,777,177, issued to Pazos, teaches a process for making double metal cyanide-catalyzed polyols involving making a polyether polyol by polymerizing an epoxide in the presence of a double metal cyanide (DMC) catalyst, a continuously added starter (Sc), and optionally, an initially charged starter (Si). The continuously added starter has at least about 2 equivalent percent of the total starter used (total starter=Sc+Si). Although conventional processes for making DMC-catalyzed polyols charge the entire starter to be used to the reactor at the start of the polymerization, the process of Pazos adds both the epoxide and the Sc continuously to the reaction mixture during the polymerization.
U.S. Pat. No. 5,059,641, issued to Hayes et al., discloses very low viscosity PMPOs having high styrene/acrylonitrile ratios and good stability which are produced with epoxy-modified polyols as dispersants. The epoxy-modified polyol dispersant may be made by one of three methods: (1) adding the epoxy resin internally to the modified polyol, (2) capping or coupling a polyol not containing an epoxy resin with such a resin, or (3) providing the epoxy resin both internally to the polyol and as a cap or coupler. Epoxy-modified polyols having a hydroxyl to epoxy ratio of about 8 or less, made by one of these techniques, are said to be superior dispersants and provide polymer polyols having higher styrene contents, improved stability and viscosity properties.
Numerous patents disclose the continuous and semi-batch preparation of PMPOs, including processes where the base polyol is a DMC-catalyzed polyol. Heretofore, as exemplified in those patents, the process is sequential, i.e., a polyol is prepared first which is reacted with unsaturated monomers in a subsequent step.
Therefore, a need exists in the art for a simultaneous process for preparing a polymer polyol (PMPO) directly from starter compound having active hydrogen atoms, alkylene oxide(s), double metal cyanide (DMC) catalyst, unsaturated monomer(s) and radical initiator(s).